Color management is a field of technology that relates to translating digital images from one media to another in order to preserve color appearance. The Commission Internationale de l'Éclairage (hereinafter “CIE”) XYZ observer functions are the basis for most color measurements that require the matching of colors. By combining these functions with non-linear color appearance models (CAMs) such as CIELAB and CIECAM96s, complex color images as well as simple color patches can be reproduced with great success. It is well known that corrections to XYZ must be performed when the measured value of white between media or environments is different. Some illustrative examples of these cross-media conversions include:                1) Converting a Red-Green-Blue (RGB) image that has been optimally prepared on a display calibrated to D65 white to a CMYK file to be printed on neutral paper and viewed in a D50 light booth;        2) Converting a CMYK file optimized for neutral white paper to be printed on custom paper that is intentionally tinted a pastel blue or pink; and        3) Converting an image which was optimized for viewing in D50 illumination for viewing in office light illuminationThe type of technology that specifically addresses this topic is known as “chromatic adaptation”. Chromatic adaptation provides a transformation from tristimulous values in one viewing condition to matching tristimulous values in a second set of viewing conditions. The “viewing condition” may be in one illustrative example the measured properties of the “white” illumination employed to view the images. However, more generally, “viewing condition” may be, for example, the measured value of white (RGB=100%) for a display system such as a computer monitor. For the purposes of this description, it is assumed that “viewing condition” is the adaptive “white point” of a scene that is being viewed. In the case of printed images on paper, the white point is the combined effect of illumination and reflective properties of the paper. In the example of images on a display, the white point is the maximum of red, green, blue (RGB=100% each or gray level 255, 255, 255) combined to yield the “whitest white” of the display system in a calibrated state.        
Several methods of chromatic adaptation have been developed in the past. The most recent version of the International Color Consortium (ICC) specification specifically recommends a Bradford model as a simple, baseline method for performing chromatic adaptation (see section 6.2.1 of the ICC Specification ICC.1: 2004-10). This was a big step forward, since previous versions of the ICC specification only defined a primitive XYZ scaling as a baseline adaptation method (see 6.3.2 of the ICC Specification ICC.1: 2004-10). This method was adequately useful for conversions between CMYK media with slightly different paper color (i.e. up to 5 delta E in a*b*), but was quite unsatisfactory, as for example, for use in converting images from displays set at a D65 white point for purposes of displaying on a system with a D50 white point (i.e. a 20 delta E difference from D50). As discussed above, defining an effective method of chromatic adaptation is key for color conversions between media and environments with significant white point differences.